The invention is based on a valve for controlling fluids in accordance with the type defined in further detail in claim 1.
Such valves for controlling fluids, in which a valve closing member divides a low-pressure region in the valve from a high-pressure region, are well known in the industry, for example in fuel injectors, especially common rail injectors, or in pumps of motor vehicles.
European Patent Disclosure EP 0 477 400 A1 also describes such a valve; it is actuatable via a piezoelectric actuator and has an arrangement for a travel converter, acting in the stroke direction, of the piezoelectric actuator; the deflection of the actuator is transmitted via a hydraulic chamber, which serves as a hydraulic booster or coupling and as a tolerance compensation element. The hydraulic chamber encloses a common compensation volume between two pistons defining the hydraulic chamber, of which one piston is embodied with a smaller diameter and is connected to a valve closing member to be triggered, and the other piston is embodied with a greater diameter and is connected to the piezoelectric actuator. The hydraulic chamber is fastened between the pistons in such a way that the actuating piston executes a stroke that is lengthened by the boosting ratio of the piston diameter, when the larger piston is moved by a certain travel distance by means of the piezoelectric actuator. Via the compensation volume of the hydraulic chamber, tolerances resulting from temperature gradients or different temperature expansion coefficients of the materials used and possible settling effects, can be compensated for without thereby causing any change in the position of the valve closing member.
The hydraulic system in the low-pressure region, in particular the hydraulic coupler, requires a system pressure, which drops because of leakage, unless hydraulic fluid is adequately replenished.
To that end, in the industry, versions of common rail injectors are known in which the system pressure is expediently generated in the valve itself and should also be kept as constant as possible upon a system start, the filling of the system pressure region is assured by the delivery of hydraulic fluid from the high-pressure region of the fuel to be controlled into the low-pressure region where the system pressure is to prevail. This filling is often done with the aid of leakage gaps, which are represented by leakage or filling pins. The system pressure is as a rule adjusted by means of a valve, and the system pressure can also be kept constant for a plurality of common rail valves, for example, as well.
However, if the system pressure in the hydraulic chamber is substantially constant, and is at least largely independent of the prevailing high pressure in the high-pressure region, there is the problem that at high pressure values, great actuator force is required to open the valve closing member counter to the high-pressure direction, which in turn dictates a correspondingly large, cost-intensive dimensioning of the piezoelectric unit. Moreover, at high pressure in the high-pressure region, the positive displacement of hydraulic volume out of the hydraulic chamber via the gaps surrounding the adjacent pistons is reinforced accordingly, meaning that under some circumstances, the refilling time for building up and maintaining the counterpressure on the low-pressure region is prolonged, so that for lack of complete refilling, in the event of a re-actuation of the valve soon thereafter, a shorter valve stroke will be executed, which can adversely affect the opening behavior of the entire valve.
The valve for controlling fluids according to the invention, as defined by the characteristics of claim 1, has the advantage that the system pressure in the hydraulic chamber is variable, and its pressure level is dependent on the pressure prevailing in the high-pressure region. Thus at a high level in the high-pressure region, an increase of the system pressure in the hydraulic chamber is possible, as a result of which the actuating piston for opening the valve closing member counter to the prevailing high pressure is reinforced. In this way, a reduced triggering voltage of the piezoelectric unit suffices, compared to a valve with constant system pressure, and therefore the valve of the invention can be equipped with a smaller, less-expensive piezoelectric unit.
The invention furthermore enables a defined refilling of the low-pressure region, especially the hydraulic chamber. If the pressure in the high-pressure region is increasing, the refilling time can be shortened with the variable system pressure.
The embodiment according to the invention is distinguished by its structural simplicity, which makes it possible for the variable system pressure in the hydraulic chamber to be defined by means of easily adjustable geometrical variables, such as the longitudinal length of the solid body of the refilling device surrounding the gap flow between the high-pressure delivery and a branching point to the hydraulic chamber.
The solid body can be disposed essentially axially immovably in the hollow chamber.
In an especially advantageous version, it can also be provided that the solid body is disposed axially adjustably in the hollow chamber by means of a mechanical adjusting device, as a result of which influences of tolerance of valve components, specifically both an individual tolerance influence and the total influence of various components, can be mechanically corrected. The valve of the invention embodied in this way can advantageously be assembled without requiring that all the component sizes be adhered to exactly.
In a preferred application of the valve of the invention as a fuel injection valve, it is furthermore possible to meet the demand for the most precise possible preinjection quantity simply by checking the preinjection quantity after assembly, and if there is a deviation from the set-point quantity, a mechanical correction is made by way of the longitudinal mobility of the solid body of the filling device. This advantageously makes it unnecessary to replace parts, which is complicated and expensive.